Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to transformers. More particular-
ly, this invention relates to miniaturized transformers suitable
for use in small-sized electrical devices such as hybrid integrated
circuit components, or small-sized modular components.
Description of the Prior Art
As demand for small-sized electrical components has
; increased over the years, there has been a corresponding need to
provide miniaturized transformers for components requiring such
elements. Generally speaking, the problem of transformer minia~
turization has been quite difficult relative to miniaturization
of other kinds of electrical elements, and this has particularly
been true where low~frequency applications are involved.
For a number of reasons, traditional transformer design
concepts have not provided a suitable basis for making such minia-
turized transformers. For example, conventional wound transformers
are difficult to make in small sizes, especially because the wind-
ings typically must be made of very tiny wire. The cost of manu-
facture also is considerable, due to the large amount of painstaking
labor required. Moreover, it has been difficult to achieve high
performance with such small-sized devices of conventional design.
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Various proposals have been made from time to time
seeking a solution to the problem of making minaturized trans-
formers, but none of these proposals has resulted in a truly
satisfactory transformer construction.
SUMMARY OF THE INVE~TION
In a preferred embodiment of the present invention to
be described hereinafter in detail, a compact transformer con-
struction is provided wherein the transformer windings are
arranged in planar spiral configuration, with each winding
embedded in a layer of solid insulating dielectric securely
attached to a rigid substrate Both the substrate and the in-
sulating dielectric are formed with a common opening about which
the windings are disposed, and a solid magnetic core extends
through that opening to form a low-reluctance closed magnetic
circuit for the transformer windings. Advantageously, a trans-
former in accordance with this invention may comprise two such
rigid substrates carrying identical sets of planar spiral wind-
ings disposed about the common solid magnetic core.
The layers of insulating dielectric and windings em-
bedded therein preferably are laid down on the substrate by
well-established thick film deposition processes. It thus is
possible to ma~e, at low cost, a rugged multi-layered transformer
structure combining small size, excellent performance, high relia-
bility, and ready adaptability to standard component assembly
techniques.
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Accordingly, it is an object of the present invention
to provide a superior transformer of small size. ~nother object
of the invention is to provide such a transformer which is capable
of economical manufacture and suitable for standard assembly
techniques. Yet another object of the invention is to provide
such a transformer which can be used for low-frequency applications
and which has high performance capa~lities including excellent
magnetic coupling, good linearity, and the ability to withstand
; high voltages between windings. Still other objects, aspects and
advantages of the invention will in part be pointed out in, and
in part apparent from, the following detailed description of a
preferred embodiment of the invention, considered together with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWI~GS
.
FIGURE 1 is a plan view of a transformer constructed in
accordance with the present invention. (~ote: The opaque layers
of insulating dielectric are not shown in this view in order to
present the general configuration of the metalliæed windings embed-
ded in the dielectric.);
FIGURE 2 is a side elevation view of the transformer
shown in Figure l;
FIGURE 3 is a vertical section taken along line 3-3
of Figure l;
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FIGURE 4 is an enlarged plan view of one substrate of
the transformer, showing -the three transformer windings as though
the insulating dielectric were transparent;
FIGURE 5 is a detail section taken along line 5-5 of
Figure 4; and
FIGURE 6 is a detail section taken along line 6-6 of
Figure 4.
'DETAILED DESCRIPTIO~ OF A PREFERRED EMBODIMENT
: Referring now to Figures 1-3, the transformer in accord-
ance with the present invention comprises first and second rigid -~_~
rectangular substrates 10 and 12 of alumina, held together in over-
lying posltion, and offset a short distance longitudinally. Each
substrate carries on one flat surface thereof a film as generally
. indicated at 14 and 16. These films comprise a series of distinct
layers of an insulating dielectric, with each layer having embedded
therein a corresponding planar spiral winding in the form generally
illustrated at 18 in Figure l. In the present embodiment, each
of the two substrates lO and 12 carries -three such winding layers,
for a total-of six transformer windings.
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The multi-layered films 14 and 16 preferably are formed
by well-known thick-film processing techniques. In one such process,
each individual winding layer of the film is developed by screen-
printing a metallization pattern, comprising a matrix of conduc-
tive particles arranged (in this case) in a spiral configuration,
and an overlay of insulating dielectric material such as a high-
temperature crystallizable glass dielectric. The screen-printed
material then is either singly or co-fired at high temperature to
complete the process.
Firing of the screen-printed material causes the con-
ductive particles of the metallization pattern to be sintered
and fused into a continuous conductor forming a planar spiral
winding such as is generally indicated at 18 in Figure 1. E'iring
also solidifies the glass insulating dielectric to form a rigid
15 pancake-like structure with the planar spiral winding embedded ~__
therein.
As noted above, each substrate 10, 12 carries three such
; winding layers. As will be described in more detail hereinbelow,
a fourth layer also is laid over the top winding layer to provide
cross-over electrical conductors for making connections from the
inner ends of the three windings to corresponding termination points
at the edge of each substrate. The screen-printing and firing
procedure is carried out for each winding layer, and also for the
fourth layer establishing the cross-over electrical connections.
Each of the four screen-printed layers ordinarily will be about
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1 mil thick (0.001"), whereas the supporting alumina substrate may
have a thickness of about .015".
The central portions of the substrates 10, 12 are enclosed
within a three-legged magnetic core 20, preferably composed of
facing, mated E-I cores adhesively secured together at the regions
of joinder. These E-I cores are asse~led to the completed sub-
strates with the central leg 22 of the E-core fitted into aligned
rectangular holes 24 (see also Figure 4) cut in the substrates prior
to the thick-film processing. The side legs 26, 28 of the E-core
extend down along the sides of the substrates to the regions of
joinder with the flat I-core, to establish closed magnetic circuits
passing through the substrate openings 24.
The screen-printed films 14, 16 applied to the substrates
10, 12 extend substantially to the edges of the central openings
24 cut in the substrates. The magnetic core leg 22 is dimensioned
to provide a reasonably close fit with the openings 24, and serves
to aid in holding the substrates in position.
As shown in Figure 1, each substrate 10, 12 is provided
at one end thereof with a set of termination pads 30, 32 for making
electrical connections to the spiral windings generally indicated
at 18. With the longitudinally offset arrangement of the substrates,
both termination pads, 30, 32 are readily accessible from the same
side of the transformer for establishing connections thereto.
~7~
It will be seen that the transformer of this invention
is especially suitable for adap-ta-tion -to hybrid in-tegrated cir-
cuit components, and can readily be mounted on a mother substrate
together with o-ther elemen-ts. Conventional connection techniques
such as wire-bonding advantageously can be used to make electrical
connection to the termination pads 30, 32. As noted above, each
subs-trate in the present embodiment carries three separa-te wind-
ings (in corresponding layers of -the -thick films 14, 16) requi-
ing six -terminals on each substrate. Such a transformer is
particularly adap-ted for use in a single--transformer isola-tor
of the type disclosed in copending Canadian Paten-t Application No.
367,616, filed on December 29, 1980 by Analog Devices, Incorporated
assignee of William H. Morong, III.
In this embodiment, bo-th subs-trates 10 and 12 are
identical, with essentially identical mul-ti-layered films 14
and 16 containing the sets of three spiral -transformer windings.
Since the winding arrangemen-ts are essen-tially iden-tical, only
one set of windings will be described hereinbelow.
Referring now -to the plan view of Figure 4 and the sec-
-tional views of Figures 5 and 6, i-t can be seen that the spiral
conductors of each of the three windings 34, 36, 38 are planar,
with adjacent turns of the spiral being uniformly spaced apart.
The conductors of -the bot-tom and -top windings 34, 38 are aligned
vertically, while the conductors of -the middle winding are offset
laterally from -those of the other two windings, -to assure optimum
spacing. Insulating dielectric 40 is laid down for each layer
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ineluding the fourth layer 42 for the eross-over eonductors.
The dieleetrie material extends between and around -the metal-
lization layers, and includes an outer layer 40a.
Referring partieularly to Figures 4 and 6, the fourth
thick-film layer 42 comprises a set of cross-over return con-
ductors such as the conduetor illustrated at 44. That eross-over
eonduetor is eonneeted at its inner end 44a to the inner end of
the eorresponding spiral winding 36 by means of a vertical con-
ductor 46. This conductor is formed in staircase fashion by a
series of metallizations earried out during formation of the
winding layers 34, 36, 38. Sueh vertical stairease eonduetor
is loeated in a eorresponding reetangular vertieal opening 50
(Figure 4) formed in the insulating dieleetrie 40 during sereen-
printing of the winding layers. The outer end 44b of the eross-
over conduetor 44 is eonnected to the corresponding -terminal ~__
point 52 of the termination pad 26 by means of a vertical conauc-
tor 54 which also is formed in stairease fashion by a series of
metallizations, just as in making the inner vertieal conductor 46.
The formation of the multiple winding layers as described
above, including the vertieal eonduetors 46 and 54, is earried out
using well-known and frequently used multi-layer thiek-film tech-
niques which are part of the established prior art in that area
of technology. Thus detailed diseussion of these techniques has
been omitted, in order to simplify the present diselosure.
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Although a specific preferred embodiment of the novel
transformer construction of the present invention has been de-
scribed hereinabove in detail, it is desired to emphasize that
this detailed description is solely for the purpose of illus-
trating the invention, and is not to be considered as limitingthe scope of the invention since it is clear that many variations
and modifications can be made by those of skill in the art in
order to meet the requirements of particular applications. For
example, transformers in accordance with the invention can be
provided with different numbers of windings, and various kinds of
conductive materials and techniques can be used to form the wind-
ings. Different types of insulating dielectric can be employed.
Also, although the described arrangement provides a single winding
in each layer, other arrangements are possible. For example,
each of two layers could carry one-half of a spiral windlng, with ~__
the complete winding being established by making vertical connec-
tion between the inner ends of the two half-windings. Additionally,
each layer could be formed with more than a single winding (or
half-winding) by using spiral interlace arrangements. Thus it
is clear that there are many ways in which to carry out the inven-
tion to obtain the important advantages thereof.
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